Electromagnetic device



Patented Dec. 29, 1931 UNITE'DISTF'IATES PAUL a. norsrne, or cnicaeo, ILINoIs, ASSIGNOR 'ro CENTRAL scmmrrrc cou- PANY, A, coaroaArIoN orILLINOIS PATENT or-Flea ELECTROMAGNETIC DEVICE Application filedDecember 12, 1929 Serial No. 413,658.

The student of physics and electricity often finds it difficult to graspthe'fundamental concepts of electromagnetism, and it is one of theprimary. objects of this invention to provide apparatus of exceedinglysimple design which may be'used' to demonstrate in an elementary andconvincing manner the printion with the accompanying drawings, in

which I 12 Fig. 1 is a plan View the apparatus; and

Fig. 2is a longitudinal, sectional view of the same taken on the line22of Fig. 1.

About a century ago, the scientist Barlow produced rotation in a starwheeliby causing "11 an electric current to traverse radially over thewheel while placed between the poles of a horse shoe magnet. I

, A few years later, Faraday discovered that he could produce anelectric current by rotating ancopper disk between the poles of a steelmagnet or electromagnet, the current flowing from shaft to rim, or vice.versaac cording to the sense of-rotation. Sliding con tacts were usedon the shaft and the periphery of the diskfto conduct away the currentgener c. i 1 i I A rotating copper disk placed/m a magnetic field atright angles to the .planeof the disk has for many years been used todemonstrate the operation of Lenzs law and the resultant efiectof amagnetic brake.

This invention combines into one apparatus a structure especiallyadapted to the requisites of pedagogics which can be used to demonstratethe classical experiments referred to above of Barlow and Faraday andthe operation of Lenzs law. I

This specific illustration and correspondingly specific description areused for the purpose of disclosure only and are not to be taken asimposing a limitation upon the scope of the invention except as requiredby the prior art.

The apparatus in one of its forms com- 1 prises a base preferably ofwood, progive to the base a convenient clearance from its means ofsupport. A permanent magnet 12, preferably of chrome steel, is removablysecured to the base by clamps 13 and 14 which are U-shaped in form andhave their upper arms of sufficient length to engage the upper face ofthe magnet as at 15.. The clamps are fastened to the base by countersunk bolts. 16 provided with securing nuts 2 17 and thumb nuts 18. p. Y

I The ends of the magnet 12 are brought close together at 19 and acopper disk20 is mounted in a jawlever 21 for'rotation between the polesof the magnet, Frictionless conical bearings 22'are provided on the jawarms for engaging the shaft 23 of the disk, and have lock nuts 24 tomaintain roper adjustment. I v

A U-shaped ulcrum piece 25 secured to the base by a screw 26carriesthelever 21 by means of the stud screws 27 and permits the diskto be raisedout of the magnetic field by simply applying pressure on the end of thelever. A pin stop 28 serves to fix the normal position of the'disk. t

The base 10 is provided with a mercury trough 29 into which the rotatingdisk 20 dips and electrical connection is made between the mercury inthe trough and the binding post 30 by a screw 31 and conductor 32. Theshaft of the rotating disk 20 is in electricalconnec- .tion with asecond binding post 33 through the lever 21, fulcrum 25, screw 26 anda-conductor 34. In this way, an electrical current can be made to passradially through the disk from the shaft to the periphery, and viceversa. 7

When the apparatusis used as an elementary electric motor, thebindingpostsBO and 33*are connected to a suitable source-of current,such as a six volt storage cell, through a rheostat capable of carryinga fairly large current; A carbon compression rheostat is well suited forthis purpose. When the current isturned onjthddisk will rotate in adirection depending upon that of the magnetic field and of the current.j A reversal of direction of either thema-gnetic field or the drivingcurrent will result in a rotationref the .diskin an opposite direction,while a reversal of both will leave the rotation unchanged.

'vided with knobs 11 at its four corners, which i I A radial stripe 35on the disk aids in clearly showing the rotation of the disk.

Faradays dynamo experiment with a rotating copper disk may be readilyshown by connecting the binding posts 30 and 31 to a gal vanometer andthen spining the disk by hand. A current is thereby induced which may bedetected by the galvanometer. At constant rotational speed, a steadydeflection will be registered on the galvanoineter, its magnitudedepending upon the strength of the magnetic field and the speed ofrotation.

The magnetic brake effect may be clearly shown by this apparatus bysetting the disk into rapid rotation when tilted out of its normalposition and then lowering it into the magnetic field. In thisexperiment, the mercury contact has no importance and the braking actionis caused solely by the fact that a conductor is being moved across amagnetic field. By the operation of Lenzs law, currents are inducedwhich tend to oppose the movement of the conductor, which in the case ofa rotating disk are called eddy currents.

Inasmuch as the magnet 12 may be readily removed from the base, it is aneasy matter to reverse the magnetic field by inverting the magnet, whichwill cause a rotation of the disk in the opposite direction in the motorexperiment and in the dynamo experiment will cause the galvanometer tobe deflected on the other side of the Zero mark. The mercury contactwhich engages the periphery of the rotating disk provides a frictionlesselectrical contact which enables a more striking demonstration of themotor and dynamo experiments to be made.

The fact that the disk may be readily moved in and out of the magneticfield provides a convenient structure for making the experiments and isexceptionally useful in the magnetic brake experiment.

I claim as my invention:

1. An electro-magnetic device comprising in combination a base, amercury trough in the base, a rotatable metallic disk dipping in themercury, bearings for the disk, means for bodily lifting the disk andbearings from the trough, and a permanent magnet having its poles 011opposite sides of the disk.

2. An electro-magnetic device comprising in combination a metallic disk,a magnet having its poles on opposite sides of the disk, and means fortemporarily removing the disk from the magnetic field, including a leverrotatably carrying the disk.

3. In a device of the class described, the combination of a rotatabledisk having an axial hub, means for setting up a magnetic field throughthe disk, and a fulcrumed support equipped with frictionless bearingsengaging the hub adapted to raise and lower the disk from the magneticfield.

4. An e1ectro-magnetie device comprising in combination a rotatablemetallic disk, a

bifurcated lever carrying the disk, a fulcrum for the lever whereby thedisk may be raised and lowered, a sliding contact for the periphery ofthe disk, adapted to be connected to an external circuit, and means forcreating a magnetic field intermediate the sliding con tact and thecenter of the disk.

5. An electro-magnetic device comprising a base, a mercury contact inthe base, a rotatable metallic disk dipping in the mercury, means forconnecting the mercury contact and the disk hub to a source ofelectrical energy to conduct a current radially through the disk, meansfor creating a magnetic field intermediate the mercury contact and thedisk hub, and a bifurcated lever carrying the disk adapted to be rockedupon its support to raise the disk out of the magnetic field.

6. In an electro-magnetic device, the combination of a base, a horseshoemagnet removably secured to the base, a metallic disk mounted forrotation between the poles of the magnet and means supported 011 thebase for removing the disk from and reinserting the same in the field ofthe magnet.

7. In a device for demonstrating certain fundamental principles ofelectro-magnetism, the combination of a base, a lever support mounted onthe base adapted to pivotally support a lever, a lever carried by thesupport equipped with arms having frictionless bearings, a metallic diskmounted be tween the arms of the lever and rotatably supported thereby,means for creating a magnetic field through the disk when the latter isin its normal operative position, said disk being adapted to be raisedfrom the magnetic field when the lever is rocked on its fulcrum.

8. In a device for demonstrating Barlows wheel, Faradays disk and theoperation of Lenzs law, the combination of a base, amercury trough inthe base, a rotatable metallic disk dipping in the mercury, means forcreating a magnetic field intermediate the mercury trough and the diskhub, and hearing supports for the disk adapted to be bodily lifted withthe disk from the magnetic fiellcil Without disturbing the rotation ofthe In testimony whereof, I aflix my slgnature.

PAUL E. KLOPSTEG.

